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Re: Psittacosaurus queries

----- Original Message -----
From: "Steve Brusatte" <dinoland@lycos.com>
To: "Alessandro Marisa" <amaris@tin.it>; <dinosaur@usc.edu>
Sent: Thursday, July 04, 2002 3:02 AM
Subject: Re: Psittacosaurus queries

> >After viewing some illustration of the skulls of various Psittacosaurus
> >species, I think that the best way is to using the term of P. Dodson
> >Horned Dinosaurs), infact in my preliminary analysis of basal
> >instead of use only Psittacosaurus mongoliensis, I've the intention to
> >all the Psittacosaurus species (with the exception of P. sattayaraki) and
> >about the condition of the antorbital fossa I using the follow character:
> >Antorbital fossa:
> >present (0):
> >present as a shallow depression or foramen (1):
> >absent (2):
>>> I am fairly sure that _Psittacosaurus_ does not possess a true
>>>fossa (or fenestra), and that this is >diagnostic of the genus.  But, am
>>>wrong here?
>>Yes, the presence of a shallow depression or a foramen instead of a true
>>antorbital fossa is diagnostic of the genus Psittacosaurus, but this is
>>my point of view.

> Interesting ideas.  In _The Dinosauria_, Sereno lists both the absence of
>an antorbital fossa and the absence >of an antorbital fenestra as
>of the Psittacosauridae.  AFAIK, only _Psittacosaurus mongoliensis_
>possesses the enigmatic depression on the maxilla, but Sereno wrote that
>"several" species possess it.  In fact, >this depression is listed as a
>separate diagnostic character for _P. mongoliensis_, but Sereno's statement
>has >me confused.  What other species might possess this feature?

Well, the condition of the absence and/or presence of an antorbital
fossa/depression in other Psittacosaurus species is as follows: the
depression seem to be present in P. mongoliensis, P. meileyingensis, P.
xinjiangensis, P. sinensis, and P. youngi, but are totally absent in P.
neimongoliensis and P. ordosensis. It is interesting to note that this
depression is well defined only in P. mongoliensis, while in P.
meileyingensis and P. xinjiangensis is shallow, and in P. sinensis and P.
youngi is extremely weak, the condition present in P. meileyingensis and P.
xinjiangensis seem to be intermediate between that in P. mongoliensis and
that in P. sinensis/P.youngi. If we accept the fact that this depression
represent a modified antorbital fossa we have a line that start with the
presence of an antorbital fossa (the condition in Neoceratopia) and stopped
to the totally absence of it, and if we accept the suggestion of HP Pete
Buchhoz that P. mongoliensis is the basal form we can conclude that the
presence of an antorbital fossa is the primitive condition within the

> It most certainly is.  This is a list of diagnostic features of the
>Psittacosauridae which I have compiled from the literature, mostly from
>Sereno's chapter in _The Dinosauria_:
> 1) Short preorbital skull segment (less than 40% of skull length)

I use this in my Neoceratopsian analysis, but for relationships of
Psittacosaurus species I use this one:
1a) Skull profile rectangular with a long preorbital region; intermediate;
rounded with short preorbital region.

> 2) external naris positioned very high on the snout, with the ventral
>margin of the external naris lying dorsal to the ventral margin of the
> 3) nasal extending rostroventrally below the external naris and
>esbablishing contact with the rostral via the rostroventral process
> 4) caudolateral premaxillary process broad, separating the maxilla from
>the external naris
> 5) premaxilla, maxilla, lacrimal, and jugal convering to a point
> 6) antorbital fenestra absent
> 7) antorbital fossa absent (maybe not so clear now...)
> 8) unossified gap in the wall of the lacrimal canal (possibly not seen in
>all species)
> 9) eminence on the rim of the buccal emargination of the maxilla near the
>junction with the jugal
> 10) elongate pterygoid mandibular ramus (I don't know too much about this
> 11) dentary crown with bulbous primary ridge
> 12) manual digit IV with only one simplified phalanx
> 13) manual digit V absent

And also:
14) lateral margin of prefrontal not upturned; strongly upturned
15) postorbital region narrow; broad
16) horizontal ridge on postorbital weak developed; strongly developed
17) anterior ramus of squamosal not extends as far as anterior wall of
supratemporal fenestra; extend to anterior wall of supratemporal fenestra
18) posterior margin of quadrate gently sulcate in lateral profile; deeply

> There might be a few more, but these are the basics.  The postcrania,
>being extremely primitive, offers little information of diagnostic value.

In regard to the postcranial you can added:
19) length of metatarsal I, 60% that of metatarsal III; 70% that of
metatarsal III.
20) tibia shorter than the skull; equal/longer than the skull.
21) Ischium shorter than the femur; longer than the femur
22) Distal end of ischium distally flattened absent; present.
Some of this postcranial characters are from personal comment to HP Rutger

Alessandro Marisa
Via Achille Grandi n°18
Rovereto (TN) ITALY
Tel: 039-0464-434658 Email: amaris@tin.it